There are many requirements for a variety of x-ray tubes. The target materials may be varied and the angular/electrical relationships in the tube may be varied to obtain the desired intensity and wavelength of x-ray emission. Useage ranges from delicate in vivo and in vitro animate tissue examination to massive industrial applications. The typical vacuum x-ray tube has a heated filament to furnish a supply of electrons which are accelerated by a very high voltage to an anode target. This target upon being struck by the high energy electrons emits x-rays. Heated filaments evaporate and grow less rigid with voltage increases; therefore, to prevent filament burnout lowered performance must be accepted or lifetimes are reduced.
Several types of x-ray tubes have been developed utilizing field effect emission. Generally, these types are some form of field effect emitter using either a single emitter or a low number of multiple array emitters which have been manually constructed, or the combination of a thermal emitter plus an intense electric field may be employed. Typical of prior art research programs in field emission is the work at Linfield College and Linfield Research Institute. Example reports are "Field Emission Cathode Ray Tube Development," by J. W. Griffith and W. W. Dolan of Linfield Research Institute, July 1958; and "Development of Field Emission Flash X-Ray Tubes and Devices" by W. P. Dyke et al, October 1961, Linfield Research Institute.
Current advances in the art of field effect electron emitters are set forth in U.S. Pat. Nos. 3,745,402 and 3,746,905 by Shelton et al and U.S. Pat. No. 3,783,325 by Shelton, co-inventors in the instant invention. The field effect electron emitter is an oxide-metal matrix comprised of ordered metal fibers separated by an insulating oxide. The emitter may be comprised of several million fibers arranged in parallel for each square centimeter of emitter surface area. The ends of the fibers form the emitting surface and are all substantially the same diameter with the distance between adjacent fiber ends being substantially the same.